In the practice of electroplating procedures, it is usually important to make sure that the material plated on the workpiece is plated uniformly. For some specific applications, uniform plating is particularly important, such as in the plating of orifice plates with an amorphous nickel phosphorus alloy, such as disclosed in copending application Ser. No. 464,101 filed Feb. 4, 1983.
In the art it is recognized that electroplating procedures may be modified by the use of a non-conductive shroud, and false anodes have been known for the purpose of leveling out current density variations while electroplating. However, it has been found according to the present invention that if a non-conductive shroud and a false anode are used in combination, platings having the desired uniformity are produced, whereas they are not necessarily produced using one or the other alone.
According to the present invention, a particular non-conductive shroud and a false anode particularly associated with the non-conductive shroud are provided so that plating of a workpiece can be accomplished with uniform electrodeposition of material (for example amorphous nickel phosphorus alloy) on the workpiece. The increased uniformity is provided by providing the non-conductive shroud so that it defines an opening adjacent the cathode-workpiece between the cathode-workpiece and the anode of the plating apparatus cell. The shroud prevents bulging of current lines beyond the opening defined thereby, causing a more desirable distribution of current density on the cathode-workpiece. The false anode is preferably connected to an open end of the shroud spaced from the cathode-workpiece, and comprises a screen of electrically conductive material which is not connected to a current source other than the electrolyte. The false anode provides an area of uniform potential at the open end of the shroud. In order to overcome the tendency for the bath liquid to stagnate within the area defined by the shroud, the bath liquid is circulated through openings formed in a closed wall of the shroud, so as to be uniformly moved over the cathode-workpiece.
According to one aspect of the present invention, there are provided: A cell including a bath having material therein to be electrodeposited on the workpiece. An anode disposed in the cell. A source of electrical current operatively connected to the anode and to a workpiece to be plated so that the workpiece acts as a cathode. Electrically insulating material shroud means operatively connected to the workpiece and defining an area between the anode and the workpiece for preventing bulging of current lines beyond the area defined thereby. And, conductive material means physically disposed between the anode and the cathode adjacent the area defined by the shroud means providing an area of uniform potential. The shroud preferably comprises a substantially quadrate (e.g. rectangular) box of electrically insulating material having first and second open ends and closed sidewalls. The electrically conductive means preferably comprises a screen mounted to the second open end of the box. A plurality of holes are defined in one of the closed sidewalls of the box, and nozzles circulate the bath liquid through the holes uniformly over the cathode-workpiece. For uniformly plating opposed faces of a workpiece, preferably two anodes, shrouds, and false anodes are provided, and the cathode-workpiece is sandwiched between the shrouds.
The invention also relates to a particular generally quadrate (e.g. rectangular) shroud of electrically insulating material which includes a generally quadrate (e.g. rectangular) box having first and second open ends, and closed sidewalls. A collar is operatively mounted to the box at the first open end thereof, and is adapted to engage the cathode-workpiece, while the false anode is mounted to the second open end of the box. A plurality of openings are formed in one of the sidewalls for the introduction of the circulating bath liquid. The collar preferably includes means for receiving a bus-bar therein, for operative connection to the cathode-workpiece.
The invention also relates to a method of uniformly plating material onto a workpiece, comprising the steps of: (a) providing a cell with a bath which includes the material to be plated; (b) immersing the workpiece in the bath; (c) providing an anode in the bath; (d) electrically connecting the anode to a source of electrical current, and supplying electrical current to the bath so that the workpiece acts as a cathode; (e) preventing bulging of current lines beyond an area defined adjacent the cathode-workpiece; and (f) maintaining a surface other than the anode substantially equidistant from the workpiece at a substantially uniform electrical potential. Step (e) is practiced by providing a shroud of electrically insulating material defining an area adjacent the cathode-workpiece, between it and the anode. Step (f) is accomplished by providing a false anode, such as an electrically conductive material screen mounted on an open end of the shroud. Bath liquid preferably uniformly circulates around the cathode-workpiece. The method is useful with almost all types of electroplating, but is particularly applicable where very uniform electroplating must be provided, such as in the electrodeposition of amorphous nickel phosphorus alloys on substrates.
It is the primary object of the present invention to provide a simple and effective apparatus and method for the uniform electroplating of workpieces. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.